Dear Science,

The idea of the body scanners at the airport pisses me off. I mean, really: Is there any way this is going to make us safer? I suspect this is all a scam to sell more military equipment to the government. Here's my question: Are these scanners safe? They use X-rays, right? That can't be good for you. I travel a ton for work, and I don't want this to stop me from having children someday.

Frequent Flyer

You're not the only one concerned about this. Four University of California, San Francisco professors—Doctors Sedat, Agard, Stroud, and Shuman—substantiate your worry.

There are two broad types of whole-body scanners used at U.S. airports. One type of scanner uses radio waves in the millimeter wavelength; the other type uses X-rays. Both work on the same broad principle: bombard your body with an electromagnetic wave and read the signal of the waves as they return. The difference is in how damaging X-rays can be, as compared to millimeter waves. Millimeter waves are nonionizing—they cannot directly damage atoms. X-rays count as ionizing radiation; they're high enough in energy to rip electrons off atoms and cause all sorts of damage. When those atoms are in your DNA, the result can be mutations. It's like the difference between being shot by a rubber bullet and a real bullet.

The manufacturers of the X-ray-based scanners claim that the dose of radiation is small, akin to the cosmic radiation one would receive on a cross-country flight or in a chest X-ray. They further claim that these machines deliver only a small, short burst of wimpy X-rays that are able to enter only the layers of the skin—and no further. These arguments are both unproven and unconvincing at this time.

Yes, the dose of radiation is the same as an airplane flight's worth of cosmic rays—but it's delivered over a much shorter period of time. When radiation comes on as a trickle over time, there's time for our cells to repair the DNA between hits. The quick burst of radiation delivered by these scanners—as opposed to the slow trickle delivered by cosmic rays—is potentially far more damaging because our cells' repair machinery could be overwhelmed by multiple points of damage at once.

Yes, the dose of radiation is similar to a chest X-ray. This type of X-ray, because the waves are strong enough to go through the body, distributes the damage more evenly. Because the waves from these scanners are absorbed entirely in the skin, the radioactive energy is concentrated there.

These are reasonable, and at this point unaddressed, risks. The deployment of backscatter X-ray whole-body scanners is a huge, unconsented radiation-dosing experiment on travelers. Science thinks you should opt out.

Irradiatingly Yours,


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